Transparent iolite (or Cordierite) is often used as a gemstone. The name "iolite" derives from the word violet in Greek. Another old name is dichroite, a Greek word meaning "two-colored rock", a reference to cordierite's strong pleochroism. It is sometimes called "water-sapphire" and "Vikings' Compass" (It has an ability to determine the sun's direction on overcast days.) Iolite varies in color from sapphire blue to blue violet to yellowish gray to light blue as the light angle changes.
Iolite is sometimes used as an inexpensive substitute for sapphire. It is less expensive as it is softer than sapphires and can be found in Sri Lanka, India, Burma, Australia's Northern Territory, Namibia, Brazil, Tanzania, Madagascar, Connecticut, and the Yellowknife area of the Northwest Territories of Canada.